The present invention relates to a copier in which the image surface of an original document being transported by an automatic document feeder (ADF) is sequentially scanned by optics for slit exporure. More particularly, the present invention is concerned with a copier which is automatically conditioned for a sheet-through mode or a sheet-stationary mode so as to perform effective copying with no regard to the desired number of copies per document.
A copier with an ADF is extensively used so that a number of documents in the form of sheets may be automatically fed one at a time to a glass platen of the copier, then scanned by optics, and then driven out of the copier to a documnt discharge tray. The ADF is usually made up of a document feed table to be loaded with a stack of documents, a separating device for separating one of the documents fed from the table from the others while transporting that document, and a belt for driving the single document onto the glass platen of the copier. A document register roller is located downstream of the separating device in order to feed the document at an adequate time toward the glass platen. The optics is usually disposed below the glass platen to be movable in a reciprocating motion and constituted by a first scanner and a second scanner. While the first scanner is loaded with a lamp and the like and movable at the same speed as a photoconductive element, the second scanner is loaded with mirrors and the like and movable at half the speed of the first scanner. The scanners of the optics individually start moving from their home positions to scan the entire surface of a document which is laid on the glass platen and then return to the home positions. When two or more copies of the same document are desired, the optics is of course reciprocally moved by the number of times which is the same as the number of copies, scanning the document during its forward strokes.
The optics does not scan a document during an interval in which the document is driven from the document register roller to the glass platen and an interval in which the scanners of the optics return to their home positions. While the returning speed of each scanner may be selected to be far higher than the scanning speed, it is impossible to increase the moving speed of the belt. Hence, as the number of copies per document decreases, the proportion of the period of time necessary for moving a document to the total copying time increases resulting in the copying ability (copies per minute of PCM) being reduced. In light of this, when a copier with an ADF is operated to produce one copy with each of a plurality of documents, a sheet-through mode is selected in which a document is moved at a predetermined speed on and along the glass platen to be scanned by the optics which is fixed in place so as to minimize the interruption of operation ascribable to the document moving time. More specifically, the sheet-through mode is such that the scanners of the optics are held in a halt at particular positions below the glass platen to scan a document which is moved over the scanners. This mode is opposite to a sheet-stationary mode in which the optics is movable to scan a document which is laid on the glass platen as previously stated.
A problem with the sheet-through mode is that when a plurality of copies are desired for each document, a document has to be manually removed from the document discharge tray and then loaded in the ADF every time a copy of the document is produced. This not only costs much labor but also aggravates the loss of time to thereby critically lower the copying ability of the copier. Although the labor may be saved by using a recirculation type automatic document feeder (RADF), the loss of time cannot be eliminated.